Sliding bias method and system for reducing idling current while maintaining maximum undistorted output capability in a single-ended pulse modulated driver

ABSTRACT

Various embodiments include a system and method that control idling current of a pulse modulated driver. The system may include an audio input device configured to receive an audio input signal. The system can include sliding bias control circuitry configured to generate a sliding bias control signal based on a level of the audio input signal. The system may include sliding bias generation circuitry configured to generate a sliding bias voltage superimposed onto the audio input signal to generate a pulse modulated driver input signal that is input into an amplifier. The sliding bias voltage may be based on the sliding bias control signal.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

The present application claims priority under 35 U.S.C. §119(e) toprovisional application Ser. No. 62/008,333 filed on Jun. 5, 2014,entitled “Sliding Bias Method of Reducing Idling Current whileMaintaining Maximum Undistorted Output Capability in a Single EndedPulse Modulated Driver.” The above referenced provisional application ishereby incorporated herein by reference in its entirety.

U.S. Pat. No. 4,592,087 issued to Killion on May 27, 1986, isincorporated by reference herein in its entirety.

U.S. Pat. No. 4,689,819 issued to Killion on Aug. 25, 1987, isincorporated by reference herein in its entirety.

U.S. Pat. No. 5,099,856 issued to Killion et al. on Mar. 31, 1992, isincorporated by reference herein in its entirety.

U.S. Pat. No. 5,131,046 issued to Killion et al. on Jul. 14, 1992, isincorporated by reference herein in its entirety.

U.S. Pat. No. 5,144,675 issued to Killion et al. on Sep. 1, 1992, isincorporated by reference herein in its entirety.

U.S. Pat. No. 6,466,678 issued to Killion et al. on Oct. 15, 2002, isincorporated by reference herein in its entirety.

U.S. Pat. No. 8,715,152 issued to Puria et al. on May 6, 2014, isincorporated by reference herein in its entirety.

U.S. Publication No. 2010/0048982 A1 by Puria et al, published on Feb.25, 2010, is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

Certain embodiments of the invention relate to controlling idlingcurrent of a pulse modulated driver. More specifically, certainembodiments of the invention relate to a sliding bias method and systemfor reducing idling current while maintaining maximum undistorted outputcapability in a single-ended pulse modulated driver.

BACKGROUND OF THE INVENTION

Pulse duration modulation, often referred to as Class D modulation, is ascheme for increasing the efficiency of power amplifiers. Increasing theefficiency of power amplifiers is especially valuable in hearing aids,where the tiny cell must provide all the power for days, weeks, ormonths. An estimated 30-50 million hearing aids have incorporated theClass D hearing aid amplifier described by Killion in U.S. Pat. Nos.4,592,087 and 4,689,819, which are incorporated by reference herein intheir entirety, often more than doubling the battery life as a result.These Class D hearing aid amplifiers are generally characterized by alow-distortion push-pull balanced bridge output ofpulse-duration-modulated pulses, and work extremely well with aninductive load that can store energy as described in the above patentdisclosures and also described briefly in Killion 1991 [Audio, v75, No.1, 42-44] and in further detail in Carlson 1988 [Hearing Instruments,v39, pp 30-32].

Killion, et al., in U.S. Pat. No. 5,099,856, which is incorporated byreference herein in its entirety, introduced a system for transmittingaudio signals via light. The system includes a transmitter module, afiber optic cable, and a receiver. The transmitter module converts aninput signal into a Class D modulated series of light pulses. The fiberoptic cable isolates the transmitter and receiver from common sources ofelectromagnetic interference. The receiver receives the light pulses andconverts them into a replica of the original signal. The system has beenimplemented, for example, as an isolation amplifier for AuditoryBrainstem Response measurements where interference is a constantproblem. With this approach, however, the efficiency of a push-pull,balanced bridge output is lost. Instead, the light source, an LED, isdriven directly with no intervening energy storage device.

A modulated light beam can also be used to transmit sufficient audiofrequency current to a magnetic hearing aid receiver or “Earlens”vibrator on the eardrum of a wearer, as described in the U.S. Pat. No.8,715,152 and U.S. Publication No. 2010/0048982 A1 by Puria et al, whichare incorporated by reference herein in their entirety. In one exampleof such an application, a modulated stream of pulses may produce anaverage LED current of 10 mA, with peak current of 20 mA. Although aClass A driver works in this application, the LED light output versuscurrent generally shows a non-linear characteristic, with lessefficiency at lower currents, creating a distortion in the demodulatedsignal. For this reason, some form of pulse modulation, such as Class Dpulse duration modulation, can provide greater linearity between theaveraged light output and the input signal because each pulse—long orshort—is at maximum light-output efficiency. If Class D peaks are set to20 mA, then 100% ON time corresponds to a continuous current of 20 mA,0% ON time produces zero current, and 50% ON time corresponds to anaverage current of 10 mA. This often is the zero-signal condition. Inthis way, the equivalent of a Class A waveform replication of theamplified input signal is obtained after the received light pulsessensed with a photodetector diode or transistor are averaged to producean audio signal.

Another problem with Class A power amplifiers is a relatively largebattery drain. Specifically, the idling current at zero signal is onehalf of the peak current, allowing a maximum sine wave waveform to gofrom the idling current to twice the idling current on one half of thepeak waveform and from the idling current to zero current on the otherhalf. Changing to pulse duration modulation does not improve thesituation in the case of a resistive or LED load. In the above LEDexample, the same average current drain of about 10 mA is needed ineither case. By using a voltage doubler, 10 mA at 2.2 V calls forapproximately 20 mA from a 1.3 V Zinc Air cell, or a total of 26 mW.Ignoring other power consumption, this would correspond to only 23 hourslife on the most powerful 675 Cochlear Zinc Air hearing aid cell. Inother words, a new battery is needed at the start of each day witheither Class A or Class D output.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with some aspects of the present invention asset forth in the remainder of the present application with reference tothe drawings.

BRIEF SUMMARY OF THE INVENTION

A system and/or method is provided for controlling idling current of apulse modulated driver, substantially as shown in and/or described inconnection with at least one of the figures, as set forth morecompletely in the claims.

These and other advantages, aspects and novel features of the presentinvention, as well as details of an illustrated embodiment thereof, willbe more fully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary pulse modulated driver forcontrolling idling current, in accordance with an embodiment of theinvention.

FIG. 2 illustrates corresponding waveforms with the sliding bias set fora low value of ON time in the output pulses, in accordance with anembodiment of the invention.

FIG. 3 illustrates corresponding waveforms with the sliding bias set for50% ON time, in accordance with an embodiment of the invention.

FIG. 4 is a block diagram of an exemplary system for controlling idlingcurrent of a pulse modulated driver, in accordance with an embodiment ofthe invention.

FIG. 5 is a diagram of exemplary circuitry of the sliding bias controlillustrated in FIG. 4 configured to dynamically change a bias voltage,in accordance with an embodiment of the invention.

FIG. 6 is a block diagram of an exemplary system for controlling idlingcurrent of a pulse modulated driver, in accordance with an embodiment ofthe invention.

FIG. 7 is a diagram of exemplary circuitry of the direct current (DC)level shift and offset adjust illustrated in FIG. 6, in accordance withan embodiment of the invention.

FIG. 8 is a graph illustrating an exemplary change in bias voltage at apercentage of ON time of a Class D modulator, in accordance with anembodiment of the invention.

FIG. 9 is a flow chart illustrating exemplary steps that may be utilizedfor controlling idling current of a pulse modulated driver, inaccordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the invention may be found in a method 200 andsystem 100 for controlling idling current of a pulse modulated driver byregulating a sliding bias voltage 38. For example, aspects of thepresent invention have the technical effect of increasing the efficiencyof a Class D modulator 160 by superimposing a sliding bias voltage 38onto the audio input signal 122 so that at low audio input signal levelsa low percentage ON time (and thus low idling current) results, whereaswhen a large audio input signal is presented, the sliding bias 38 canquickly rise towards 50% ON time of the pulse train, maintaining lowaudible distortion under all conditions.

The foregoing summary, as well as the following detailed description ofcertain embodiments will be better understood when read in conjunctionwith the appended drawings. To the extent that the figures illustratediagrams of the functional blocks of various embodiments, the functionalblocks are not necessarily indicative of the division between hardwarecircuitry. Thus, for example, one or more of the functional blocks(e.g., processors or memories) may be implemented in a single piece ofhardware (e.g., a general purpose signal processor or a block of randomaccess memory, hard disk, or the like) or multiple pieces of hardware.Similarly, the programs may be stand alone programs, may be incorporatedas subroutines in an operating system, may be functions in an installedsoftware package, and the like. It should be understood that the variousembodiments are not limited to the arrangements and instrumentalityshown in the drawings. It should also be understood that the embodimentsmay be combined, or that other embodiments may be utilized and thatstructural, logical and electrical changes may be made without departingfrom the scope of the various embodiments of the present invention. Thefollowing detailed description is, therefore, not to be taken in alimiting sense, and the scope of the present invention is defined by theappended claims and their equivalents.

As used herein, an element or step recited in the singular and proceededwith the word “a” or “an” should be understood as not excluding pluralof said elements or steps, unless such exclusion is explicitly stated.Furthermore, references to “an embodiment,” “one embodiment,” “arepresentative embodiment,” “an exemplary embodiment,” “variousembodiments,” “certain embodiments,” and the like are not intended to beinterpreted as excluding the existence of additional embodiments thatalso incorporate the recited features. Moreover, unless explicitlystated to the contrary, embodiments “comprising,” “including,” or“having” an element or a plurality of elements having a particularproperty may include additional elements not having that property.

Furthermore, the term processor or processing unit, as used herein,refers to any type of processing unit that can carry out the requiredcalculations needed for the invention, such as single or multi-core:CPU, DSP, FPGA, ASIC, ARM processor, or a combination thereof.

FIG. 1 is a block diagram of an exemplary pulse modulated driver forcontrolling idling current, in accordance with an embodiment of theinvention. Referring to FIG. 1, there is shown inputs of a single-endedClass D amplifier 160, comprising a saw tooth waveform 150, an audiosignal 122, and a sliding bias input (V_(BIAS)) 38. In an exemplaryembodiment, the saw tooth waveform 150 is applied to one side of thedifferential comparator 156 and an audio signal 122 is applied to theother side of the differential comparator 156. The audio signal 122 canbe decoupled by a capacitor 152. A sliding bias input (V_(BIAS)) voltage38 is added to the audio input signal 122 to control the idle percentageON time of the Class D amplifier 160. While a differential input isshown for the modulator, a single ended input may be alternativelyimplemented, with the saw tooth 150, the audio signal 122, and a biassignal 38 combined at a single input, provided only that thepeak-to-peak saw tooth waveform 150 exceeds the peak-to-peak AC signalinput 122. The sliding bias 38 may provide a relatively low value ofidle current without affecting the small-signal output of the modulatorsince the audio signal 122 is capacitor 152 decoupled. The value ofV_(BIAS) 38 corresponding to the switched output waveform of FIG. 1 hasbeen chosen for a 50-50 on-off time, where ON is full supply voltage andOFF is 0 volts, for example.

FIG. 2 illustrates corresponding waveforms (a), (b) with the slidingbias set for a low value 14 of ON time in the output pulses 16, inaccordance with an embodiment of the invention. Referring to FIG. 2,there is shown (a) a saw tooth waveform 150 having a maximum peakcurrent 10, a zero current 12, and a 5% of maximum peak current idlecurrent 14. Also shown is (b) a pulse modulated waveform with 5% ON timepulses 16. With a dissipative load such as a light emitting diode (LED),a 5% ON time corresponds to one tenth the average current delivered witha 50% ON time, the latter also referred to as a 50-50 duty cycle.

In an exemplary embodiment, the peak current 10 of an LED may be 20 mA,so the average current delivered with 50% ON time is 10 mA. In contrast,the average current delivered with a 5% ON time is 1 mA. In dailypractice, the 5% ON time idle is used the majority of the time. Forexample, if the 50% condition allows 110 dB output, the 5% conditionwould allow 90 dB undistorted signal output. In typical hearing aidapplications, the gain for loud sounds is typically reduced to zero forsounds in the 90-110 dB region because these sounds are loud enough, andsometimes too loud, for both normal hearing and hearing-impairedindividuals, and adding gain could be uncomfortable for a wearer of thehearing aid.

FIG. 3 illustrates corresponding waveforms (a), (b), (c) with thesliding bias 14 set for 50% ON time, in accordance with an embodiment ofthe invention. Referring to FIG. 3, there is shown (a) a saw toothwaveform 150 having a maximum peak current 10, a zero current 12, and a50% of maximum peak current 14. Also shown are (b) square wave outputpulses 18 with no signal input, showing 50% ON time. Still referring toFIG. 3, there is shown (c) a waveform illustrating a maximum undistorteddemodulated signal output 20 for a 1 kHz sine wave input just beforeclipping sets in. In various embodiments, the sliding bias voltage 38 isset low when the input signal 122 is low so the output pulse ON time is,for example, 5% or less the majority of the time. The V_(BIAS) is rampedup to 50%, as shown in FIG. 3, so the idling current is 50% of the peakcurrent when the input signal 122 exceeds a selected level, such as asound pressure level or other suitable criteria. For example, if thepeak current is 20 mA, the average idling current is 10 mA for 50% ONtime. The average idling current for 5% ON time is 1 mA, a 10 to 1reduction in idling battery drain.

FIG. 4 is a block diagram of an exemplary system 100 for controllingidling current of a pulse modulated driver, in accordance with anembodiment of the invention. Referring to FIG. 4, the system 100comprises an audio source 110, a front end amplifier 120, sliding biascontrol 130, a saw tooth waveform generator 150, a Class D amplifier160, and a light emitting diode (LED) 170. The audio source 110 can be amicrophone, a direct audio input such as from a media player, atelecoil, or any suitable input mechanism for receiving sound and/or anaudio signal. The audio input signal 122, or sound converted into anaudio input signal 122, is provided to the front end amplifier 120.

In various embodiments, the front end amplifier 120 may comprisesuitable logic, circuitry, interfaces and/or code that may be operableto amplify the audio input signal 122. For example, the front endamplifier 120 may provide alternating current (AC) amplification of theaudio input signal 122. As another example, the front end amplifier 120can provide direct current (DC) level shift and offset adjust to theaudio input signal 122. In an exemplary embodiment, the front endamplifier 120 may be a “K-AMP” as described in U.S. Pat. No. 5,131,046,by Killion, et al., which is incorporated by reference herein in itsentirety. In certain embodiments, the front end amplifier 120 can be adigital signal processor that executes an algorithm, code, and/orinstructions, for example, to provide the appropriate amplification. Forexample, the digital signal processor may be a “DigiK” processor asdisclosed in U.S. Pat. No. 6,466,678, by Killion et al., which isincorporated by reference herein in its entirety, and also described inthe DigiK Manufacturing Software and Fitting Software manual publishedby Etymotic Research, Inc. in September 2002. Still referring to FIG. 4,the AC amplified and DC shifted audio input signal 122 may be providedto the sliding bias control 130, which can be implemented in analog ordigital.

In various embodiments, the sliding bias control 130 may comprisesuitable logic, circuitry, interfaces and/or code that may be operableto generate a sliding bias control signal that is used to generate asliding bias voltage. FIG. 5 is a diagram of exemplary analog circuitryof the sliding bias control 130 illustrated in FIG. 4 configured todynamically change a bias voltage, in accordance with an embodiment ofthe invention. Referring to FIG. 5, an audio input signal 122 may be ACamplified and DC shifted by front end amplifier 120 as discussed above.The bias control signal can be generated, for example, by a rectifier32, with capacitor 34 and resistor 36 determining the recovery timeconstant. In certain embodiments, rectifier 32, which may be a Shockleydiode, for example, is engaged and the capacitor 34 is quickly broughtup to a voltage on bias output 38 corresponding to 50% idling current ifa sudden large audio input signal 122 is received. The bias voltageV_(BIAS) 38 drifts back down following the R-C time constant determinedby capacitor 34 and resistor 36 to the lower idling current, such as 5%,if the loud audio input signal 122 is reduced.

Referring again to FIG. 4, the sliding bias control 130 may additionallyand/or alternatively be implemented as a digital signal processor thatexecutes an algorithm, code, and/or instructions, for example, toprovide a control signal that increases or decreases the bias 38proportional to the level, or other suitable characteristic, of theaudio input signal 122. The bias 38 is increased to provide anundistorted output signal corresponding with the audio input signal 122.With a digital implementation of the sliding bias control 130, theapplication of the audio input signal 122 may be delayed to provide agradual and therefore less audible increase in the bias 38. The delaymay be approximately 10 ms, which is defined as between 5 and 30 ms,such that a delay in the audio input signal 122 may not be noticeable toa listener.

In certain embodiments, the sliding bias control 130 can additionallyand/or alternatively be derived from the adaptive compression circuit ofthe K-AMP 120 described in U.S. Pat. No. 5,144,675 by Killion et al.,which is incorporated by reference herein in its entirety. In such anembodiment, the sliding bias voltage 38 recovers slowly to the low-idlestate after a prolonged loud sound, to avoid “pumping,” but recoversquickly for a short loud sound, to avoid “off the air” sounds. Asdescribed below with respect to FIGS. 6 and 7, the sliding bias controlsignal may be provided from the compression ratio control output of theK-AMP 120.

Referring to FIG. 4, the sliding bias control 130 outputs a generatedsliding bias voltage 38 that is added to the audio input signal 122 tocontrol the idle percentage ON time of the modulator. A saw toothwaveform generator provides a saw tooth waveform 150 to one side of adifferential comparator 156 and the sliding bias voltage 38 superimposedonto the audio input signal 122 is provided at the other side of thedifferential comparator 156. The output of the comparator 156 isprovided to the amplifier 160, such as a single-ended Class D amplifier,for example. Alternatively, the saw tooth waveform 150, audio signal122, and bias signal 38 may be combined at a single input and providedto the amplifier 160.

In various embodiments, the amplifier 160 may comprise suitable logic,circuitry, interfaces and/or code that may be operable to generate apulse modulated output signal that drives a light emitting diode (LED)170. In various embodiments, the LED 170 may comprise suitable logic,circuitry, interfaces and/or code that may be operable to generate amodulated light beam to transmit the audio signals, for example. Certainembodiments provide a voltage doubling circuit between the amplifier 160and the LED 170. For example, if the LED 170 calls for 2 Volts or moreand a 1.25 Volt cell voltage is desired, a voltage doubler circuit, suchas described in U.S. Pat. No. 5,099,856 by Killion et al., which isincorporated by reference herein in its entirety, may be implemented toprovide nearly constant drive voltage to LED 170.

In various embodiments, the sliding bias single-ended Class Dimplementation can be obtained in software with any pulse-modulationscheme incorporated in a digital hearing aid circuit. For example,instructions, code, and/or algorithms may be provided that dynamicallyshifts the pulse modulation to increase the idling current so themaximum signal capability is correspondingly increased if a calculatedlevel of the audio input signal 122 exceeds a threshold set for the lowidling current. Furthermore, the recovery time and attack time constantscan be determined by clock counting rather than from physicalresistor-capacitor(s) time constants. Accordingly, the sound quality ofthe digital hearing aid can be substantially indistinguishable from theanalog version of the sliding bias control circuitry as shown by thefidelity ratings of the K-AMP and DigiK illustrated in FIG. 4 ofKillion, “Myths that Discourage Improvements in Hearing Aid Design,”Hearing Review, Volume 11, p. 38, January 2004.

The exemplary system 100 for controlling idling current of a pulsemodulated driver of FIG. 4 shares various characteristics with theexemplary pulse modulated driver for controlling idling currentillustrated in FIG. 1 and described above.

FIG. 6 is a block diagram of an exemplary system 100 for controllingidling current of a pulse modulated driver, in accordance with anembodiment of the invention. Referring to FIG. 6, the system 100comprises an audio source 110, a front end amplifier 120, DC level shiftand offset adjust 140, a saw tooth waveform generator 150, a Class Damplifier 160, and a light emitting diode (LED) 170. The audio source110, also referred to as an audio input device, can be a microphone, adirect audio input such as from a media player, a telecoil, or anysuitable input mechanism for receiving sound and/or an audio signal. Theaudio input signal 122, or sound converted into an audio input signal122, is provided to a front end amplifier 120.

In various embodiments, the front end amplifier 120 may comprisesuitable logic, circuitry, interfaces and/or code that may be operableto amplify the audio input signal 122. For example, the front endamplifier 120 may provide alternating current (AC) amplification of theaudio input signal 122. In certain embodiments, the front end amplifier120 can be a digital signal processor that executes an algorithm, code,and/or instructions, for example, to provide the appropriateamplification. Additionally and/or alternatively, the front endamplifier 120 may be a “K-AMP” as described in U.S. Pat. No. 5,131,046,by Killion, et al., which is incorporated by reference herein in itsentirety. The K-AMP amplifier 120 includes a variable recovery timecircuit for use with wide dynamic range automatic gain control, commonlyknown as “adaptive compression.” The DC voltage available from thecompression ratio control (CRC) output on the K-AMP circuit 120 canprovide the appropriate time constant for a sliding bias control of theidling current of the Class D amplifier 160 via the DC level shift andoffset adjust 140. Similarly, the appropriate time constant for thesliding bias control can be obtained by a digital processor, such as theDigiK referred to above.

In various embodiments, the DC level shift and offset adjust 140 maycomprise suitable logic, circuitry, interfaces and/or code that may beoperable to provide direct current (DC) level shift and offset adjust tothe output of the front end amplifier 120, such as the compression ratiocontrol (CRC) output on the K-AMP circuit 120. In certain embodiments,the DC level shift and offset adjust 140 can be a digital signalprocessor that executes an algorithm, code, and/or instructions, forexample, to provide the appropriate level shift and offset. Additionallyand/or alternatively, the DC level shift and offset adjust 140 may becircuitry, for example, as illustrated in FIG. 7.

FIG. 7 is a diagram of exemplary circuitry of the direct current (DC)level shift and offset adjust 140 illustrated in FIG. 6, in accordancewith an embodiment of the invention. Referring to FIG. 7, the DC levelshift and offset adjust 140 comprises transistors 40, 42 and resistors44, 46, 48 that provide the DC level shift and offset to generate thesliding bias voltage (V_(BIAS)) 38. For example, the voltage from thecompression ratio control (CRC) output of K-AMP 120 may be approximatelyzero volts for audio input signals 122 of 90 dB SPL and greater, andapproximately 0.3 Volts for quiet audio input signals 122 of 40-60 dBSPL.

In various embodiments, resistor 46 may be selected so that with nocurrent flowing in transistor 42, the idling ON time will be about 50%(e.g., 0.45 Volts in FIG. 8), the normal operating condition for fullsignal hearing aid applications. The voltage at the emitter of NPNtransistor 42 is approximately equal to the voltage at the compressionratio control (CRC) output on the K-AMP circuit 120 that is applied tothe base of PNP transistor 40, provided that both come from a compatibleintegrated circuit process and have appropriate emitter areas, sinceboth have similar operating current. Accordingly, for loud signals of 90dB SPL and above, for example, the current in transistor 42 is zero anddoes not interfere with the 50% ON time set by resistor 46.

In certain embodiments, resistor 48 can be selected so that for quietsignals the current in transistor 42 can pull the bias voltage 38 toabout 0.3 V as shown in FIG. 8, so the percentage ON time of the outputpulses is about 5% to 10%. The sliding bias control voltage 38 may beintroduced without affecting the normal signal flow to the Class Damplifier 160 by applying a constant-current source from transistor 42.In this way, the adaptive compression circuitry of the K-AMP front endamplifier 120 can provide appropriate time constants for the slidingbias control voltage 38 and provide the wide-dynamic-range-compressionoperation of the K-AMP front end amplifier 120.

Referring again to FIG. 6, the DC level shift and offset adjust 140outputs a generated sliding bias voltage 38 that is added to the audioinput signal 122 to control the idle percentage ON time of themodulator. A saw tooth waveform generator provides a saw tooth waveform150 to one side of a differential comparator 156 and the sliding biasvoltage 38 superimposed onto the audio input signal 122 is provided atthe other side of the differential comparator 156. The output of thecomparator 156 is provided to the amplifier 160, such as a single-endedClass D amplifier, for example. Alternatively, the saw tooth waveform150, audio signal 122, and bias signal 38 may be combined at a singleinput and provided to the amplifier 160.

In various embodiments, the amplifier 160 may comprise suitable logic,circuitry, interfaces and/or code that may be operable to generate apulse modulated output signal that drives a light emitting diode (LED)170. In various embodiments, the LED 170 may comprise suitable logic,circuitry, interfaces and/or code that may be operable to generate amodulated light beam to transmit the audio signals, for example. Certainembodiments provide a voltage doubling circuit between the amplifier 160and the LED 170 that provide nearly constant drive voltage to LED 170.

The exemplary system 100 for controlling idling current of a pulsemodulated driver of FIG. 6 shares various characteristics with theexemplary system 100 for controlling idling current of a pulse modulateddriver illustrated in FIGS. 1 and 4 as described above.

FIG. 8 is a graph illustrating an exemplary change in bias voltage at apercentage of ON time of a Class D modulator, in accordance with anembodiment of the invention. Referring to FIG. 8, a bias 38 of 0.3 Voltscorresponds to 5% ON time, while 0.45 Volts bias 38 produces the 50% ONtime corresponding to loud audio input signals 122.

FIG. 9 is a flow chart 200 illustrating exemplary steps 202-216 that maybe utilized for controlling idling current of a pulse modulated driver,in accordance with an embodiment of the invention. Referring to FIG. 9,there is shown a flow chart 200 comprising exemplary steps 202 through216. Certain embodiments of the present invention may omit one or moreof the steps, and/or perform the steps in a different order than theorder listed, and/or combine certain of the steps discussed below. Forexample, some steps may not be performed in certain embodiments of thepresent invention. As a further example, certain steps may be performedin a different temporal order, including simultaneously, than listedbelow.

In step 202, an audio input signal 122 is received. For example, theaudio input signal 122 may be received at an audio input device 110,such as a microphone, telecoil, direct audio input, or any suitablemechanism for receiving an audio input signal 122.

In step 204, the audio input signal 122 is amplified. For example, theaudio input signal 122 may be provided to a front end amplifier 120. Thefront end amplifier 120 may provide alternating current (AC)amplification of the audio input signal 122. The front end amplifier 120can also provide direct current (DC) level shift and offset adjust tothe audio input signal 122. The front end amplifier 120 may includelogic, circuitry, interfaces, and/or code. For example, the front endamplifier 120 can be a digital signal processor, a “K-AMP” as describedin U.S. Pat. No. 5,131,046, by Killion, et al., which is incorporated byreference herein in its entirety, or any suitable circuitry.

In step 206, a level of the audio input signal 122 is measured. Forexample, the AC amplified and DC shifted audio input signal 122 may beprovided to a sliding bias control 130. The sliding bias control 130 maycomprise suitable logic, circuitry, interfaces and/or code that may beoperable to measure a level of the audio input signal 122. For example,a rectifier 32 may be engaged in response a sudden large audio inputsignal 122 being received that exceeds a threshold. As another example,a digital signal processor may execute an algorithm, code, and/orinstructions to measure the level, such as the sound pressure level orother suitable characteristic, of the audio input signal 122.

In step 208, a sliding bias control signal is generated based on themeasured level of the audio input signal 122. For example, a slidingbias control 130 may comprise suitable logic, circuitry, interfacesand/or code that may be operable to generate a sliding bias controlsignal that is used to generate a sliding bias voltage 38 based on ameasured level or other suitable characteristic of the audio inputsignal 122. The bias control signal can be generated by a rectifier 32,where the rectifier becomes engaged in response a sudden large audioinput signal 122 being received that exceeds a threshold. As anotherexample, the sliding bias control 130 may be implemented as a digitalsignal processor that executes an algorithm, code, and/or instructionsto provide the bias control signal that increases or decreases the bias38 proportional to the level, such as the sound pressure level or othersuitable characteristic, of the audio input signal 122. As a furtherexample, the sliding bias control signal can be derived from theadaptive compression circuit of the K-AMP 120 described in U.S. Pat. No.5,144,675 by Killion et al., which is incorporated by reference hereinin its entirety. Specifically, the sliding bias control signal may beprovided from the compression ratio control output of the K-AMP 120.

In step 210, a sliding bias voltage is generated based on the slidingbias control signal. For example, the sliding bias control 130 maycomprise suitable logic, circuitry, interfaces and/or code that may beoperable to generate a sliding bias voltage 38 based on the sliding biascontrol signal. The capacitor 34 of sliding bias control circuitry 130may be quickly increased to a voltage on bias output 38 corresponding to50% idling current if, for example, rectifier 32 is engaged in responsea large audio input signal 122 being received. The bias voltage V_(BIAS)38 can be decreased following the R-C time constant determined bycapacitor 34 and resistor 36 to the lower idling current, such as 5%, ifthe loud audio input signal 122 is reduced. As another example, asliding bias voltage can be generated based on a digital signalprocessor that executes an algorithm, code, and/or instructions, forexample, to provide a control signal that increases or decreases thebias 38 proportional to the level, or other suitable characteristic, ofthe audio input signal 122. As a further example, the sliding biascontrol signal may be provided from the compression ratio control outputof the K-AMP 120 to a DC level shift and offset adjust 140 thatcomprises suitable logic, circuitry, interfaces and/or code that may beoperable to provide direct current (DC) level shift and offset adjust tothe compression ratio control (CRC) output on the K-AMP circuit 120. TheDC level shift and offset adjust 140 can be a digital signal processorand/or circuitry, for example, that outputs the sliding bias voltage.

In step 212, a pulse modulated driver input signal is generated bycombining the sliding bias voltage 38 and the audio input signal 122.For example, the sliding bias control 130 or DC level shift and offsetadjust 140 outputs a generated sliding bias voltage 38 that is added tothe audio input signal 122 to control the idle percentage ON time of themodulator. A saw tooth waveform generator provides a saw tooth waveform150 to one side of a differential comparator 156 and the sliding biasvoltage 38 superimposed onto the audio input signal 122 is provided atthe other side of the differential comparator 156. Alternatively, thesaw tooth waveform 150, audio signal 122, and bias signal 38 may becombined at a single input.

In step 214, the pulse modulated driver input signal is provided to anamplifier 160 to produce a pulse modulated output signal. For example,the output of the comparator 156 is provided to the amplifier 160, suchas a single-ended Class D amplifier, for example. Alternatively, the sawtooth waveform 150, audio signal 122, and bias signal 38 may be combinedat a single input and provided to the amplifier 160.

In step 216, the pulse modulated output signal is provided to a lightemitting diode (LED) 170. For example, an amplifier 160 may comprisesuitable logic, circuitry, interfaces and/or code that may be operableto generate a pulse modulated output signal that drives a light emittingdiode (LED) 170. In an exemplary embodiment, a voltage doubling circuitis positioned between the amplifier 160 and the LED 170 to providenearly constant drive voltage to LED 170. The LED 170 may comprisesuitable logic, circuitry, interfaces and/or code that may be operableto generate a modulated light beam to transmit the audio signals, forexample.

Aspects of the present invention provide a system 100 and method 200 forcontrolling idling current of a pulse modulated driver. In accordancewith various embodiments of the invention, the system 100 comprises anaudio input device 110 configured to receive an audio input signal 122.The system 100 comprises sliding bias control circuitry 130 configuredto generate a sliding bias control signal based on a level of the audioinput signal 122. The system 100 comprises sliding bias generationcircuitry 130 configured to generate a sliding bias voltage 38superimposed onto the audio input signal 122 to generate a pulsemodulated driver input signal that is input into an amplifier 160. Thesliding bias voltage 38 is based on the sliding bias control signal.

In a representative embodiment, the audio input device 110 comprises atleast one of a microphone, a telecoil, and a direct audio input. Incertain embodiments, the amplifier 160 is a Class D amplifier. Invarious embodiments, the system 100 comprises a front end amplifier 120configured to provide alternating current amplification of the audioinput signal 122. In a representative embodiment, the front endamplifier 120 is configured to provide direct current level shift andoffset adjust to the audio input signal 122. In certain embodiments, thefront end amplifier 120 comprises the sliding bias control circuitry130. In various embodiments, the sliding bias generation circuitry 130comprises direct current level shift and offset adjust circuitry 140configured to provide direct current level shift and offset adjust togenerate a sliding bias voltage 38.

In certain embodiments, the sliding bias control circuitry 130 comprisesa rectifier 32 configured to generate the sliding bias control signal ifthe level of the audio input signal 122 exceeds a threshold. In variousembodiments, the system 100 comprises a differential comparator 156configured to receive a saw tooth waveform 150 and the sliding biasvoltage 38 superimposed onto the audio input signal 122 to generate thepulse modulated driver input signal. In a representative embodiment, asaw tooth waveform 150, the audio input signal 122, and the sliding biasvoltage 38 are combined at a single input and provided to the amplifier160.

Various embodiments provide a method 200 for controlling idling currentof a pulse modulated driver. The method 200 comprises receiving 202 anaudio input signal 122 at an audio input device 110. The method 200comprises generating 208 a sliding bias control signal at a sliding biascontrol 130 based on a level of the audio input signal 122. The method200 comprises generating 212 a pulse modulated driver input signal bysuperimposing a sliding bias voltage 38 onto the audio input signal 122based on the sliding bias control signal. The method 200 comprisesproviding 214 the pulse modulated driver input signal to an amplifier160.

In a representative embodiment, the method 200 comprises providing 204,at a front end amplifier 120, at least one of alternating currentamplification of the audio input signal 122, and direct current levelshift and offset adjustment of the audio input signal 122. In certainembodiments, the method 200 comprises measuring 206 the level of theaudio input signal 122. In various embodiments, the method 200 comprisesgenerating 212 a pulse modulated driver output signal at the amplifier160. In a representative embodiment, the method 200 comprises providing216 the pulse modulated driver output signal to a light emitting diode170.

In certain embodiments, the method 200 comprises generating 216 amodulated light beam to transmit audio signals at the light emittingdiode 170. In various embodiments, the amplifier 160 is a Class Damplifier. In a representative embodiment, the generating 212 a pulsemodulated driver input signal comprises inputting a saw tooth waveform150 and the sliding bias voltage 38 superimposed on the audio inputsignal 122 into a differential comparator 156. In certain embodiments,the generating 212 a pulse modulated driver input signal comprisescombining a saw tooth waveform 150, the sliding bias voltage 38, and theaudio input signal 122 at a single input. In various embodiments, thesliding bias control 130 is a digital signal processor.

Certain embodiments provide a non-transitory computer-readable mediumhaving stored thereon computer executable instructions wherein theinstructions perform steps 202-216 for controlling idling current of apulse modulated driver. The non-transitory computer-readable mediumcomprises instructions for receiving 202 an audio input signal 122. Thenon-transitory computer-readable medium comprises instructions forcalculating 206 a level of the audio input signal 122. Thenon-transitory computer-readable medium comprises instructions forcomparing 208 the calculated level with a predetermined threshold. Thenon-transitory computer-readable medium comprises instructions forshifting 210, 212 an input of an amplifier 160 corresponding with idlingcurrent based on the comparison.

In a representative embodiment, the non-transitory computer-readablemedium comprises instructions for generating 214 a pulse modulateddriver output signal at the amplifier 160. In various embodiments, thenon-transitory computer-readable medium comprises instructions forgenerating 216 a modulated light beam to transmit audio signals based onthe pulse modulated driver output signal. In certain embodiments, theamplifier 160 is a Class D amplifier.

As utilized herein the term “circuitry” refers to physical electroniccomponents (i.e. hardware) and any software and/or firmware (“code”)which may configure the hardware, be executed by the hardware, and orotherwise be associated with the hardware. As used herein, for example,a particular processor and memory may comprise a first “circuit” whenexecuting a first one or more lines of code and may comprise a second“circuit” when executing a second one or more lines of code. As utilizedherein, “and/or” means any one or more of the items in the list joinedby “and/or”. As an example, “x and/or y” means any element of thethree-element set {(x), (y), (x, y)}. As another example, “x, y, and/orz” means any element of the seven-element set {(x), (y), (z), (x, y),(x, z), (y, z), (x, y, z)}. As utilized herein, the term “exemplary”means serving as a non-limiting example, instance, or illustration. Asutilized herein, the terms “e.g.,” and “for example” set off lists ofone or more non-limiting examples, instances, or illustrations. Asutilized herein, circuitry is “operable” to perform a function wheneverthe circuitry comprises the necessary hardware and code (if any isnecessary) to perform the function, regardless of whether performance ofthe function is disabled, or not enabled, by some user-configurablesetting.

Other embodiments of the invention may provide a computer readabledevice and/or a non-transitory computer readable medium, and/or amachine readable device and/or a non-transitory machine readable medium,having stored thereon, a machine code and/or a computer program havingat least one code section executable by a machine and/or a computer,thereby causing the machine and/or computer to perform the steps asdescribed herein for controlling idling current of a pulse modulateddriver.

Accordingly, the present invention may be realized in hardware,software, or a combination of hardware and software. The presentinvention may be realized in a centralized fashion in at least onecomputer system, or in a distributed fashion where different elementsare spread across several interconnected computer systems. Any kind ofcomputer system or other apparatus adapted for carrying out the methodsdescribed herein is suited. A typical combination of hardware andsoftware may be a general-purpose computer system with a computerprogram that, when being loaded and executed, controls the computersystem such that it carries out the methods described herein.

The present invention may also be embedded in a computer programproduct, which comprises all the features enabling the implementation ofthe methods described herein, and which when loaded in a computer systemis able to carry out these methods. Computer program in the presentcontext means any expression, in any language, algorithm, code ornotation, of a set of instructions intended to cause a system having aninformation processing capability to perform a particular functioneither directly or after either or both of the following: a) conversionto another language, code or notation; b) reproduction in a differentmaterial form.

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.

What is claimed is:
 1. A system configured to control idling current ofa pulse modulated driver, the system comprising: an audio input deviceconfigured to receive an audio input signal; sliding bias controlcircuitry configured to generate a sliding bias control signal based ona level of the audio input signal; and sliding bias generation circuitryconfigured to generate a sliding bias voltage superimposed onto theaudio input signal to generate a pulse modulated driver input signalthat is input into an amplifier, wherein the sliding bias voltage isbased on the sliding bias control signal.
 2. The system of claim 1,wherein the audio input device comprises at least one of: a microphone,a telecoil, and a direct audio input.
 3. The system of claim 1, whereinthe amplifier is a Class D amplifier.
 4. The system of claim 1,comprising a front end amplifier configured to provide alternatingcurrent amplification of the audio input signal.
 5. The system of claim4, wherein the front end amplifier is configured to provide directcurrent level shift and offset adjust to the audio input signal.
 6. Thesystem of claim 4, wherein the front end amplifier comprises the slidingbias control circuitry.
 7. The system of claim 6, wherein the slidingbias generation circuitry comprises direct current level shift andoffset adjust circuitry configured to provide direct current level shiftand offset adjust to generate a sliding bias voltage.
 8. The system ofclaim 1, wherein the sliding bias control circuitry comprises arectifier configured to generate the sliding bias control signal if thelevel of the audio input signal exceeds a threshold.
 9. The system ofclaim 1, comprising a differential comparator configured to receive asaw tooth waveform and the sliding bias voltage superimposed onto theaudio input signal to generate the pulse modulated driver input signal.10. The system of claim 1 wherein a saw tooth waveform, the audio inputsignal, and the sliding bias voltage are combined at a single input andprovided to the amplifier.
 11. A method for controlling idling currentof a pulse modulated driver, the method comprising: receiving an audioinput signal at an audio input device; generating a sliding bias controlsignal at a sliding bias control based on a level of the audio inputsignal; generating a pulse modulated driver input signal bysuperimposing a sliding bias voltage onto the audio input signal basedon the sliding bias control signal; and providing the pulse modulateddriver input signal to an amplifier.
 12. The method of claim 11,comprising providing, at a front end amplifier, at least one of:alternating current amplification of the audio input signal, and directcurrent level shift and offset adjustment of the audio input signal. 13.The method of claim 11, comprising measuring the level of the audioinput signal.
 14. The method of claim 11, comprising generating a pulsemodulated driver output signal at the amplifier.
 15. The method of claim14, comprising providing the pulse modulated driver output signal to alight emitting diode.
 16. The method of claim 11, comprising generatinga modulated light beam to transmit audio signals at the light emittingdiode.
 17. The method of claim 11, wherein the amplifier is a Class Damplifier.
 18. The method of claim 11, wherein the generating a pulsemodulated driver input signal comprises inputting a saw tooth waveformand the sliding bias voltage superimposed on the audio input signal intoa differential comparator.
 19. The method of claim 11, wherein thegenerating a pulse modulated driver input signal comprises combining asaw tooth waveform, the sliding bias voltage, and the audio input signalat a single input.
 20. The method of claim 11, wherein the sliding biascontrol is a digital signal processor.
 21. A non-transitorycomputer-readable medium having stored thereon computer executableinstructions wherein the instructions perform steps for controllingidling current of a pulse modulated driver, comprising: receiving anaudio input signal; calculating a level of the audio input signal;comparing the calculated level with a predetermined threshold, andshifting an input of an amplifier corresponding with idling currentbased on the comparison.
 22. The non-transitory computer-readable mediumof claim 21, comprising generating a pulse modulated driver outputsignal at the amplifier.
 23. The non-transitory computer-readable mediumof claim 22, comprising generating a modulated light beam to transmitaudio signals based on the pulse modulated driver output signal.
 24. Thenon-transitory computer-readable medium of claim 21, wherein theamplifier is a Class D amplifier.